Apparatus and systems for correcting deformations of the spine often comprise one or more rods extending along a portion of the spine. In the example of the sacral region of the spine, such rod(s) are usually fixed to the sacrum of the patient by way of a plate which, for instance, may straddle vertebrae S1 and S2 and bear a protrusion on which apparatus such as a slotted connector is fitted and immobilized. Such a slotted connector may be itself traversed by a rod and immobilize the latter by a wedging action. An example of such a plate is described in document WO-A-02/38061, for example.
It is also known to provide a plate which is fixed not on two vertebrae such as S1 and S2, but on one vertebra (for example S1) and on iliac bone of the patient. For this purpose, the plate may include, at one of its ends, a lateral extension provided with an orifice for the passage of a bone anchoring screw. This lateral extension is oriented in the direction of an iliac bone and is thus situated outside the plane of the plate, with which it normally forms an angle of the order of 50 degrees. In this way, the iliac bone can be connected to the rod. Different sizes of these sacral plates with iliac extension are available and are used in accordance with the morphology of the patient. However, the adaptation of the plate to the exact morphology of the patient is often only approximate.